Bonding and structural variations in doped Bi2Sn2O7

The structural properties of Y-doped Bi2Sn2O7 have been determined by Rietveld analysis of powder neutron and synchrotron X-ray diffraction data, These materials form a series of cubic pyrochlore-type oxides with a distinct miscibility gap at low Bi contents and show lame deviations from Vegards law, Temperature-dependent structural studies of (BiY)Sn2O7 and (BiYb) Sn2O7 have been undertaken. The structure of the high temperature, pyrochlore phase of Bi2Sn2O7 has been refined using powder neutron diffraction data. The evolution of the charge density on the Bi site has been probed using a combination of bond valence sum calculations and electronic spectroscopy. (C) 1997 Academic Press.